tableview reloadData在解包可选值时崩溃意外发现的nil

Posted 2021-04-19

我无法理解为什么reloadData（）行崩溃时出现以下错误'unjrapping optional value时意外发现nil'（另外，为什么它是可选的？）。基本上，当用户点击一个按钮时它会触发一个API请求，显示第二个VC（recipesVC），当从API检索数据时，在receivedRecipes方法（之前的VC）中我想从recipesVC（currentVC）重新加载数据我的数据是正确的传递给recipesVC，我不明白为什么reloadData（）不能在同一个VC上工作。你能帮我一点帮忙吗？谢谢。

    override func viewDidLoad() {
    super.viewDidLoad()

    let recipes = Notification.Name(rawValue: "gotRecipes")
    NotificationCenter.default.addObserver(self, selector: #selector(receivedRecipes),name: recipes, object: nil)
}

@objc func receivedRecipes() {
    let recipesVC = storyboard?.instantiateViewController(withIdentifier: "recipesList") as! RecipesViewController
    recipesVC.recipesList = request.recipeDetails
    recipesVC.recipes.reloadData()
}

答案

 @objc func receivedRecipes() {
     NotificationCenter.default.post(name: NSNotification.Name(rawValue: "recipes"), object: nil, userInfo: ["data":request.recipeDetails])

 } 

在你当前的VC中

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(self, selector: #selector(receivedRecipes(notification:)),name: NSNotification.Name(rawValue: "recipes"), object: nil)
}

 @objc func receivedRecipes(notification: Notification) {
    recipesList = notification.userInfo
    recipes.reloadData()
 }

另一答案

为您的数据添加验证：

func receivedRecipes() {
    guard let details = request.recipeDetails else { return }
    let recipesVC = storyboard?.instantiateViewController(withIdentifier: "recipesList") as! RecipesViewController
    recipesVC.recipesList = details
    recipesVC.recipes.reloadData()
}

下一个提示，您可以更新您的通知并从notification.object获取食谱，但之前您应该将它们粘贴到：

let parsedRecipes = Recipes()
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "gotRecipes"), object: parsedRecipes, userInfo: nil) 

在初始化之后还显示recipesVC：self.present(...)或self.navigationController?.show(...)